In electrophotographic copying, an electrostatic latent image is formed on a primary image-forming member such as a photoconductive surface and is developed with a thermoplastic toner powder to form a toner image. The toner image is thereafter transferred to a receiver such as a sheet of paper, plastic or the like and the toner image is subsequently fused to the receiver in a fusing station using heat, pressure, or both. The fuser station includes fuser members, which typically are rollers, although fuser belts and the like may also be used. The essential function performed in the fusing section is the application of heat and pressure to the toner image on the receiver to fix the image to the receiver.
The fusing step is commonly carried out by passing the toner image-bearing receiver between a pair of engaged rollers that produce an area of pressure contact known as a fusing nip. In order to form the nip, at least one of the rollers typically includes a compliant or conformable layer. Heat is transferred from at least one of the rollers to the toner in the fusing nip causing the toner to partially melt and attach to the receiver. In the case where the fuser member is a heated roller, a resilient compliant roller having a smooth surface is typically used.
Where the fuser member is in the form of a belt, such as a flexible endless belt that passes around the heated roller, it typically has a smooth, hardened outer surface.
Most fuser stations, which are known as simplex fusers, attach toner to only one side of the receiver at a time. In such fusers, it is common for a first one of the two rollers to be driven rotatably by an external source. The second roller is then rotatably driven by frictional contact with the first roller. Similarly, heat is typically applied to only one of the rollers. The heat may be applied by the use of one or more heater rollers to heat the exterior of the heated fuser roller or the heat may be supplied internally to the heated fuser roller.
Two basic types of heated rollers have been used. One uses a conformable or compliant pressure roller to form a fusing nip against a hard, heated fuser roller. The other uses a compliant fuser roller to form the nip against a hard, heated and relatively non-conformable pressure roller. A fuser roller designed as compliant typically includes a conformable layer having a thickness greater than about 2 millimeters (mm) and in some instances greater than about 25 mm. A fuser roller designated as “hard” includes a rigid cylinder that may have a relatively thin polymeric or conformable elastomeric coating less than about 1.25 mm thick on its exterior. There are certain advantages associated with both compliant and non-compliant rollers.
Typically, fuser rollers include a conformable layer that may be formed of any suitable material such as, for instance, polydimethylsiloxane elastomer.
Typically, toner fuser rollers include a hollow cylinder core, which is often metallic, with a roller cushion layer formed about the roller. Such cushion layers are commonly made of silicone rubbers or silicone polymers having a low surface energy, such as polydimethylsiloxane, which minimize adherence of toner to the roller, especially the heated roller. It is also known that cured polyfluorocarbon polymers and copolymers may be used to coat the cushion layer surface to further reduce the tendency of the toner to adhere to the roller and minimize contact of release oils with the cushion layer.
The cushion layer may include fillers including inorganic particles such as metals, metal oxides, metal hydroxides, metal salts, mixtures thereof and the like. These materials function to improve the thermoconductivity of the cushion layer.
The filler particles may also strengthen or otherwise modify the physical properties of the cushion material. A wide variety of rollers have been produced in attempts to more economically produce rollers that are more effective in selected desired applications. For instance, one such roller for use in a fuser station and including a flexible strengthening band, a base cushion layer around the strengthening band, a stiffening layer around the base cushion and a release layer around the stiffening layer is disclosed in U.S. Pat. No. 6,393,249B1 issued May 21, 2002, to Muhammed Aslam, et al., and assigned to NexPress Solutions, LLC. This patent is hereby incorporated by reference.
It is also known that various fluoropolymers, such as thermoplastic fluorocarbon polymers and random copolymers, are useful as coatings on such rollers. Some such fluorocarbon thermoplastic polymers and thermoplastic random copolymers, including various additive materials, are disclosed in U.S. Pat. No. 6,355,352B1 issued Mar. 12, 2002, to Jiann-Hsing Chen, et al., and assigned to NexPress Solutions, LLC and U.S. Pat. No. 6,429,249B1 issued Aug. 6, 2002, to Jiann-Hsing Chen, et al., and assigned to NexPress Solutions, LLC. These patents are hereby incorporated by reference.
While silicone rubbers and silicone polymers have been used widely as cushion layers, they have also, in some instances, been used as an exterior layer. Fluoroelastomers and rubbers such as rubbers made of ethylene propylene diene monomers and the like have also been used as cushion layer materials. Unfortunately in many fusing processes the exterior of the fuser roller, in direct contact with the toner, particularly a heated fuser roller, is coated with a release oil during fusing. Such release oils are generally detrimental to the silicone rubbers and silicone polymers. Polyfluorocarbon polymers and random copolymers coated over the outside of the cushion layer have been found to be resistant to such oils and to provide a low energy surface which readily releases from the toner on the receiver and are not adversely affected by commonly used release oils.
Continued efforts have been directed to the development of replaceable fuser members for fuser rollers in electrophotographic applications. As will be readily appreciated, improvements in the properties of surface release roller performance with respect to its conformance to the other roller used to create the pressure nip and reductions in the cost of the production of the rollers and increased ease of installation and replacement, are major factors which have been the object of continuing efforts for improvement.